The present invention relates to a drilling tool, and particularly to a drilling tool which is clamped in a chuck of a drilling machine. More particularly, the invention relates a drilling tool for forming holes in a support structure for insertion and anchoring therein fastening elements having end spreading portions.
Drills are known which include a shank which is connected to a drilling machine and adapted to be driven into rotation about its axis to form a hole in a support structure, and a drill bit at one end of the drill shank and having cutting edges projecting substantially radially of the axis and beyond the drill shank, the drill bit being adapted for increasing the cross-sectional area of the hole so as to provide in the area of the hole beyond the drill shank an undercut. For forming such an undercut, the drill is subjected to swiveling or rocking movement when the drill is advanced to the desired hole depth.
The conventional drilling tools of the type under consideration are provided with a stop plate which engages the surface of the support structure and receives contact pressure occuring during the drill and swivelling operations.
It is a well-known practice to displace a stop sleeve of the stop plate along the drill shank and to fix the sleeve on the drill shank in a predetermined position, for example by a stud bolt in order to adapt the drill for drilling holes of different depth. The stud bolt connecting the stop sleeve to the shank is normally inserted into the wall of the stop sleeve. However, such manner of fixing of the stop sleeve on the shank has been found suitable only for use in soft building materials where no percussion drilling machines are required. For drilling holes with undercut portions in concrete, or cement, or masonry percussion drills are utilized. The problem with these otherwise satisfactory installations in which the stop sleeve is fixed on the drill shank by means of a stud bolt or similar fixing means, is that since the stop sleeve is subjected to displacements, the stud bolt is breaking loose or being sheared off due to the percussion effect.
Also in the known designs the drill shank is directly clamped in the drill chuck of the drilling machine. The relatively long drill shank clamped, for example in a jaw chuck of the drilling machine, when used in hammer or percussion drills, is in addition provided with adapters for the drill chuck of the hammer drill. The utilization of special adapters as well as means for fixing the stop sleeve on the drill shank make the cost of the drill rather high. It is also known that drill shanks being a wear part of the drilling tool should be frequently replaced. All of this indicates that drilling of holes having undercut portions with an increased cross-section by the conventional drilling tools is rather expensive.